Solid-state battery and method for producing solid-state battery

ABSTRACT

The present invention provides: a solid-state battery which is not susceptible to decrease of the discharging capacity even if charge and discharge are repeated; and a method for producing a solid-state battery, which enables the achievement of a good bonded interface between a solid electrolyte layer and a anode layer by a simple process. 
     A solid-state battery  1  according to the present invention is provided with a cathode layer  20,  a anode layer  30  and a solid electrolyte layer  40  that is arranged between the cathode layer  20  and the anode layer  30.  The anode layer  30  is provided with an aluminum layer  31  that is in contact with the solid electrolyte layer  40,  a lithium layer  32,  and an aluminum-lithium alloy layer  33  that is arranged between the aluminum layer  31  and the lithium layer  32.

This application is based on and claims the benefit of priority fromJapanese Patent Application No. 2018-016548, filed on 1 Feb. 2018, andJapanese Patent Application No. 2018-016551, filed on 1 Feb. 2018, thecontent of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a solid-state battery comprising acathode electrode layer, an anode electrode layer and a solidelectrolyte layer and a method for producing the solid-state battery.

BACKGROUND ART

Conventionally, anodes containing an aluminum-lithium alloy areconsidered to have a high capacity, but when the anodes are used in alithium ion battery using a general organic solvent, the lithium-ionbattery is considered to have a low durability because LiAl is ionizedand eluted into the solvent or is micronized by repetition of charge anddischarge (see, for example, Non-Patent Document 1).

Therefore, even if an aluminum-lithium alloy is used as an anode of alithium-ion battery, it was difficult to take advantage of intrinsiccharacteristics of the aluminum-lithium alloy.

On the other hand, the aluminum-lithium alloy is expected as a materialfor an anode of a solid-state battery using no organic solvents or thelike.

For example, a technique has been proposed in which an anode electrodelayer of a solid-state battery is formed by press molding asulfide-based solid electrolyte material and a powdery aluminum-lithiumalloy (see, for example, Patent Document 1).

Further, as a method of manufacturing a solid-state battery, a method ofassembling a solid-state battery by stacking and joining the constituentlayers of the solid-state battery has been proposed (see, for example,Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Application, PublicationNo. 2014-154267

Patent Document 2: Japanese Unexamined Patent Application, PublicationNo. 2012-256436

Non-Patent Document

Non-Patent Document 1: L. Y. Beaulieu et al., “Colossal ReversibleVolume Changes in Lithium Alloys”, Electrochemical and Solid-StateLetters, 4(9), A137-A140 (2001)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in an anode electrode layer using a powdery aluminum-lithiumalloy, repetition of charge and discharge results in declination indischarging capacity.

In addition, a solid-state battery comprising an anode electrode layerformed of a powdery aluminum-lithium alloy and a solid electrolyte hasthe possibility that application of a solid electrolyte material on theanode electrode layer in a step of assembling the solid-state batteryresults in exfoliation at an interface between the solid electrolytelayer and the anode electrode layer and this results in deterioration ofthe performance of the solid-state battery. Therefore, a step ofapplying two or more layers of a solid electrolyte material (two-layerapplication) on the anode electrode layer was required, making themanufacturing process complicated.

It is an object of the present invention to provide a solid-statebattery in which the discharging capacity does not easily decline evenafter repeated charging and discharging. It is also an object of thepresent invention to provide a method for producing a solid-statebattery in which a good junction interface between the solid electrolytelayer and the anode electrode layer is obtained by a simple process.

Means for Solving the Problems

A first aspect of the present invention relates to a solid-state batterycomprising a cathode electrode layer, an anode electrode layer, and asolid electrolyte layer disposed between the cathode electrode layer andthe anode electrode layer, in which the anode electrode layer comprisesan aluminum layer in contact with the solid electrolyte layer, a lithiumlayer and an aluminum-lithium alloy layer disposed between the aluminumlayer and the lithium layer.

A second aspect of the present invention relates to the solid-statebattery as described in the first aspect, in which the film thickness ofthe anode electrode layer may be 10 to 400 μm.

A third aspect of the present invention relates to the solid-statebattery as described in the first or second aspect, in which a molarratio of lithium to aluminum, Li:Al, in the anode electrode layer may be30:70 to 80:20.

A fourth aspect of the present invention relates to the solid-statebattery as described in any one of the first to third aspects, in whichthe solid electrolyte layer may be a sulfide-based solid electrolytematerial.

A fifth aspect of the present invention relates to a method formanufacturing a solid-state battery comprising a cathode electrodelayer, an anode electrode layer comprising an aluminum layer and alithium layer, and a solid electrolyte layer disposed between thecathode electrode layer and the anode electrode layer,

-   -   the method comprising: a step of applying a solid electrolyte        material to an aluminum plate for forming the aluminum layer to        form the solid electrolyte layer; and a step of press joining a        laminate to obtain the solid-state battery, with the laminate        being obtained by disposing the cathode electrode layer on the        solid electrolyte layer formed on one surface of the aluminum        plate, and disposing a lithium plate for forming the lithium        layer on the other surface of the aluminum plate on which the        solid electrolyte layer is not formed.

A sixth aspect of the present invention relates to the method formanufacturing a solid-state battery as described in the fifth aspect, inwhich the method may further comprise a step of cutting the press joinedsolid-state battery to a predetermined length under compression.

A seventh aspect of the present invention relates to the method formanufacturing a solid-state battery as described in the fifth or sixthaspect, in which the step of press joining may be performed by a rollpressing method.

Effects of the Invention

(1) The solid-state battery of the present invention comprises a cathodeelectrode layer, an anode electrode layer, and a solid electrolyte layerdisposed between the cathode electrode layer and the anode electrodelayer, with the anode electrode layer comprising an aluminum layer incontact with the solid electrolyte layer, a lithium layer, and analuminum-lithium alloy layer disposed between the aluminum layer and thelithium layer.

Since the aluminum layer which constitutes the anode electrode layercontacts with the solid electrolyte layer, when the solid-state batteryis discharged, lithium in the lithium layer moves toward the solidelectrolyte side, but the lithium forms an alloy with aluminum in thealuminum layer before reaching the solid electrolyte layer. This canprevent lithium from flowing out from the solid electrolyte layer sidedue to discharging.

Even when the solid-state battery is repeatedly charged and discharged,formation of alloy of aluminum and lithium proceeds, and therebydecrease in aluminum from the anode electrode layer can be suppressed.

This enables provision of a solid-state battery in which the dischargingcapacity does not easily decline even if charge and discharge isrepeated.

(2) In the solid-state battery as described in the first aspect, theanode electrode layer has a suitable film thickness of 10 to 400 μm, andthis can suppress charge and discharge from decreasing aluminum andlithium from the anode electrode layer.

Thereby, it is possible to provide a solid-state battery in which thedischarging capacity does not easily decline even after repeatedcharging and discharging.

(3) In the solid-state battery as described in the first or secondaspect, a molar ratio of lithium and aluminum, Li:Al, in the anodeelectrode layer is 30:70 to 80:20, and this suppresses charge anddischarge from forming an α-LiAl phase, in which aluminum is excessiveor a monophase of lithium in the aluminum-lithium alloy, and thereby analuminum-lithium alloy layer with an appropriate blending ratio can beformed. Thus, it is possible to provide a solid-state battery in whichthe discharging capacity does not easily decline even after repeatedcharging and discharging.

(4) In the solid-state battery as described in any one of the first tothird aspects, the solid electrolyte layer is a sulfide-based solidelectrolyte material, and thereby the aluminum-lithium alloy is notionized to a solid electrolyte nor is eluted, unlike a lithium ionbattery which uses an organic solvent and in which an aluminum-lithiumalloy is used as the anode. Thereby, high durability can be maintained.

Thus, it is possible to provide a sulfide-based solid-state battery, inwhich the discharging capacity does not easily decline even afterrepeated charging and discharging.

(5) The method for manufacturing a solid-state battery, which is anotheraspect of the present invention, comprises: a step of applying a solidelectrolyte material to an aluminum plate for forming an aluminum layerto form a solid electrolyte layer; and a step of press joining alaminate to obtain the solid-state battery, with the laminate beingobtained by disposing a cathode electrode layer on the solid electrolytelayer formed on one surface of the aluminum plate, and disposing alithium plate for forming a lithium layer on the other surface of thealuminum plate on which the solid electrolyte layer is not formed.Thereby, the solid electrolyte material is directly applied to thealuminum plate which constitutes the anode electrode layer, and thisenables obtainment of a good junction interface between the solidelectrolyte layer and the anode electrode layer.

Further, the solid electrolyte material in a state of being directlyapplied on the aluminum plate is press joined at once together with thelithium plate and the cathode electrode layer to obtain the solid-statebattery.

Therefore, according to the fifth aspect, a step of directly applying asolid electrolyte layer to an anode electrode layer (or a cathodeelectrode layer) comprising a powdery active material and a solidelectrolyte itself does not exist nor is a step of re-application of ananode which has been already coated (two-layer application) necessary.

Therefore, it is possible to manufacture a solid-state battery having agood junction interface between the solid electrolyte layer and theanode electrode layer by a simple and convenient process.

(6) Since the method for manufacturing a solid-state battery asdescribed in the fifth aspect further comprises a step of cutting thepress joined solid-state battery to a manufacture a solid-state batteryhaving a good junction interface between the solid electrolyte layer andthe anode electrode layer.

(7) In the method for manufacturing a solid-state battery as describedin the fifth or sixth aspect, the step of press joining is performed bya roll pressing method. Thereby, it is possible to manufacture asolid-state battery having a good junction interface between the solidelectrolyte layer and the anode electrode layer by a simple andconvenient press joining method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view illustrating a cross section of asolid-state battery according to one embodiment of the presentinvention;

FIG. 2 is a drawing showing discharging capacity retention rates ofExample 1 and Comparative Example 1 for each cycle;

FIG. 3 is a drawing showing changes in DCR resistances of Example 1 andComparative Example 1 for each cycle;

FIG. 4 is an X-ray diffraction spectra of Example 1 before and after acycle test;

FIG. 5 is an X-ray diffraction spectra of Comparative Example 1 beforeand after a cycle test.

FIG. 6 is a drawing showing changes in discharging capacity retentionrates of Examples 2 to 6 for each cycle;

FIG. 7 is a phase diagram of an aluminum-lithium alloy of atwo-component system;

FIG. 8 is an explanatory view illustrating a method for manufacturingthe solid-state battery according to an embodiment of the presentinvention;

FIG. 9 is an explanatory view illustrating an example of the cuttingstep in the method for manufacturing a solid-state battery according toone embodiment of the present invention;

FIG. 10 is a cross-sectional SEM image of the solid-state battery ofExample 1 after charge and discharge of 100 cycles; and

FIG. 11 is a cross-sectional SEM image of the solid-state battery ofComparative Example 1 after charge and discharge of 100 cycles.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

<Solid-State Battery>

Hereinafter, one embodiment of the solid-state battery of the presentinvention will be described in detail, with reference to drawings.

FIG. 1 is an explanation drawing showing a cross section of thesolid-state battery according to one embodiment of the presentinvention.

As indicated in FIG. 1, a solid-state battery 1 comprises a battery body10, an anode current collector 50 and a cathode current collector 60.

Note that, in the present specification, the solid-state battery refersto a battery all of which is solidified.

The anode current collector 50 and the cathode current collector 60 areconductive plate-like members that hold the battery body 10 from bothsides.

The anode current collector 50 has function of collecting current of ananode electrode layer 30 and the cathode current collector 60 hasfunction of collecting current of a cathode electrode layer 20.

Electrode current collector materials to be used in the anode currentcollector 50 are not particularly limited and any conductive materialcan be used. Examples include copper, nickel, stainless steel, vanadium,manganese, iron, titanium, cobalt, zinc, etc., and among them, copperand nickel are preferable, because they have excellent conductivity andexcellent current collecting properties.

A shape and thickness of the anode current collector 50 are notparticularly limited so far as the shape and thickness are within anextent that allows the anode electrode layer 30 to collect current.

Examples of the electrode current collector materials to be used in thecathode current collector 60 include vanadium, aluminum, stainlesssteel, gold, platinum, manganese, iron, titanium, etc. and among them,aluminum is preferred.

A shape and thickness of the cathode current collector 60 are notparticularly limited so far as the shape and thickness are within anextent that allows the cathode electrode layer 20 to collect current.

The battery body 10 comprises a cathode electrode layer 20 functioningas a cathode, an anode electrode layer 30 functioning as an anode, and aconductive solid electrolyte layer 40 located between the cathodeelectrode layer 20 and the anode electrode layer 30.

The anode electrode layer 30 has an aluminum layer 31, a lithium layer32 and an aluminum-lithium alloy layer 33 disposed between the aluminumlayer 31 and the lithium plate 32.

The cathode electrode layer 20 is disposed on a solid electrolyte layer40 formed on one surface of the aluminum layer 31 in the press joiningstep, which is to be explained below.

In the present embodiment, the cathode electrode layer 20 is formed bypress molding a material containing a cathode active material and asulfide-based solid electrolyte.

Examples of the cathode active material include layered cathode activematerials such as LiCoO2, LiNiO2, LiCo1/3Ni1/3Mn1/3O2, LiVO2, LiCrO2,etc.; spinel type cathode active materials such as LiMn2O4,Li(Ni0.25Mn0.75)2O4, LiCoMnO4, Li2NiMn3O8, etc.; and olivine typecathode active materials such as LiCoPO4, LiMnPO4, LiFePO4, etc.

The sulfide-based solid electrolyte material used in the cathodeelectrode layer 20 typically contains metal element (M), which becomesconducting ions, and sulfur (S).

Examples of the M include Li, Na, K, Mg, Ca, etc. and among others, Liis preferred.

In particular, the sulfide-based solid electrolyte material preferablycomprises Li, A (A is at least one selected from the group consisting ofP, Si, Ge, Al and B) and S.

Moreover, the A is preferably P (phosphorus).

Further, the sulfide-based solid electrolyte material may includehalogen such as Cl, Br, I, etc.

This is because inclusion of halogen improves ion conductivity. Thesulfide-based solid electrolyte material may comprise O.

Examples of the sulfide-based solid electrode material having Li ionconductivity include, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O,Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr,Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3,Li2S-P2S5-ZmSn (provided that m and n are positive numbers; Z is any oneof Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-LixMOy(provided that x and y are positive numbers; M is any one of P, Si, Ge,B, Al, Ga and In), etc.

Note that the recitation “Li2S-P2S5” refers to a sulfide-based solidelectrolyte material formed by using a raw material compositioncomprising Li2S and P2S5 and this applies to other recitations.

Further, when the sulfide-based solid electrolyte material is one formedby using a raw material composition comprising Li2S and P2S5, a ratio ofLi2S with respect to a total of Li2S and P2S5 is preferably within arange of, for example, 70 mol % to 80 mol %, more preferably 72 mol % to78 mol %, and most preferably 74 mol % to 76 mol %.

This is because such a range allows the sulfide-based solid electrolytematerial to have an ortho composition or a composition close thereto,allowing the sulfide-based solid electrolyte material to be chemicallystable.

In this regard, the term “ortho” generally refers to an oxo acid havingthe highest degree of hydration in different oxo acids obtained byhydrating a single oxide.

In the present embodiment, a crystal composition of a sulfide to whichthe largest amount of Li2S is added is referred to an ortho composition.

In a Li2S-P2S5 system, Li3PS4 corresponds to the ortho composition.

In a case in which the solid electrolyte material is a Li2S-P2S5-basedsulfide-based solid electrolyte material, a ratio of Li2S and P2S5,Li2S:P2S5, for obtaining the ortho composition is 75:25 on a molarbasis.

Note that when Al2S2 or B2S3 is used instead of P2S5 in theabove-mentioned raw material composition, a preferred range is asdescribed above.

In Li2S-Al2S3 and Li2S-B2S3 systems, Li3AlS3 and Li3BS3 correspond tothe ortho compositions, respectively.

In addition, when the sulfide-based solid electrolyte material is formedby using a raw material composition containing Li2S and SiS2, a ratio ofLi2S to a total of Li2S and SiS2 is preferably within a range of, forexample, 60 mol % to 72 mol %, more preferably within a range of 62 mol% to 70 mol %, and most preferably within a range of 64 mol % to 68 mol%. This is because such a range allows the sulfide-based solidelectrolyte material to have an ortho composition or a composition closethereto, allowing the sulfide-based solid electrolyte material to bechemically stable.

In a Li2S-SiS2 system, Li4SiS4 corresponds to the ortho composition.

In a case of Li2S-SiS2-based sulfide-based solid electrolyte materials,a ratio of Li2S and SiS2, Li2S:SiS2, for obtaining an ortho compositionis 66.6:33.3 on a molar basis.

Note that when GeS2 is used instead of SiS2 in the above-mentioned rawmaterial composition, the preferred range is as described above.

In Li2S-GeS2 system, Li4GeS4 corresponds to the ortho-composition.

In addition, when the sulfide-based solid electrolyte material is formedby using a raw material composition containing LiX (X=Cl, Br, I), aratio of LiX is preferably within a range of, for example, 1 mol % to 60mol %, more preferably within a range of 5 mol % to 50 mol %, and mostpreferably within a range of 10 mol % to 40 mol %.

Further, the sulfide-based solid electrolyte material may be a sulfideglass, a crystallized sulfide glass, or a crystalline material obtainedby a solid phase method.

Note that the sulfide glass can be obtained, for example, bymechanically milling (ball milling or the like) a raw materialcomposition.

Further, the crystallized sulfide glass can be obtained, for example, bysubjecting a sulfide glass to a heat treatment at temperatures higherthan or equal to the crystallization temperature.

In addition, when the sulfide-based solid electrolyte material is a Liion conductor, the Li ion conductivity at room temperature ispreferably, for example, 61×10−5 S/cm or more, and more preferably1×10−4 S/cm or more.

In addition to the above-described sulfide-based solid electrolyte andcathode active material, the cathode electrode layer 20 may contain aconductivity-imparting material, a binder and a solid electrolyte.

The anode electrode layer 30 in this embodiment is a member comprisingthe aluminum layer 31 in contact with the solid electrolyte layer 40,the lithium layer 32 in contact with the anode current collector 50, andthe aluminum-lithium alloy layer 33 disposed between the aluminum layer31 and the lithium layer 32.

The aluminum layer 31 is a layer comprising aluminum as a maincomponent.

The lithium layer 32 is a plate-like, foil-like or thin film-like layercontaining lithium as a main component.

The aluminum-lithium alloy layer 33 is a plate-like, foil-like or thinfilm-like layer which is formed when the solid-state battery 1 ischarged, when the solid-state battery 1 is discharged, when aluminum andlithium are press molded, or when the solid-state battery 1 ismanufactured by a joining step to be described below, or the like.

Incidentally, in this specification, the aluminum-lithium alloy layer 33is not limited to a layer comprising an aluminum-lithium alloy as a maincomponent, but also includes a portion serving as a starting point forforming an aluminum-lithium alloy.

In this embodiment, the anode electrode layer 30 consists of thealuminum layer 31, the lithium layer 32, and the aluminum-lithium alloylayer 33 alone.

The anode electrode layer 30 is formed by press molding, for example, aplate-like (foil-like, thin film-like) aluminum and lithium.

Thereby, the anode electrode layer 30 containing the aluminum layer 31,the lithium layer 32 and the aluminum-lithium alloy layer 33 is formed.

Note that the anode electrode layer 30 may be formed by vapor-depositinglithium to a plate-like (foil-like or thin film-like) aluminum by asputtering method or the like.

The aluminum layer 31 is in contact with the solid electrolyte layer 40.

Here, when the solid-state battery 1 is discharged, lithium in thelithium layer 32 moves toward a solid electrolyte layer 40 side, butlithium is alloyed with aluminum in the aluminum layer 31 beforereaching the solid electrolyte layer 40. Therefore, discharging makes ithard for lithium to flow out from the solid electrolyte layer 40 side.

On the other hand, the lithium layer 32 is in contact with the anodecurrent collector 50.

For this reason, when the solid-state battery 1 is charged, aluminum inthe aluminum layer 31 moves toward an anode current collector 50 side,but aluminum forms an alloy with lithium in the lithium layer 32 beforereaching the anode current collector 50.

Therefore, charging makes it difficult for aluminum to flow out from theanode current collector 50 side.

Having the anode electrode layer 30 as described above promotesformation of an alloy of aluminum and lithium (allows thealuminum-lithium alloy layer 33 to grow), even when the solid-statebattery 1 is repeatedly charged and discharged, and this can suppressaluminum and lithium from decreasing from the anode electrode layer 30.

Thus, it is possible to obtain a solid-state battery 1 in which thedischarging capacity does not easily decline even after repeatedcharging and discharging. lithium alloy is used, aluminum is consideredto decrease from an anode due to charge and discharge.

This phenomenon is considered to be due to outflow of aluminum from theanode current collector side by charging.

Therefore, if charge and discharge is repeated using a powderyaluminum-lithium alloy, the aluminum-lithium alloy is considered to beunable to exhibit intrinsic properties thereof, and to result in, forexample, decrease in the discharging capacity.

Here, a film thickness of the anode electrode layer 30 is notparticularly limited, but in this embodiment, the film thickness is 10to 400 μm, and preferably 20 to 200 μm.

Further, at a stage prior to charge and discharge, the film thickness ofthe aluminum layer is, for example, 5 to 200 μm, and is preferably 10 to100 μm.

Furthermore, at a stage prior to charge and discharge, a film thicknessof a lithium layer is, for example, 5 to 200 μm, and is preferably 10 to100 μm.

The film thickness of the anode electrode layer 30 coming to be includedin an appropriate range makes it possible to further suppress charge anddischarge from decreasing aluminum and lithium from the anode electrodelayer 30.

Further, the film thickness of the aluminum layer 31 coming to beincluded in an appropriate range makes it possible to further suppress adecrease in lithium from the anode electrode layer 30 duringdischarging.

Furthermore, the film thickness of the lithium layer 32 coming to beincluded in an appropriate range makes it possible to further suppress adecrease in aluminum from the anode electrode layer 30 during charging.

In addition, molar and mass ratios of lithium to aluminum in the anodeelectrode layer 30 are not particularly limited. In this embodiment, themolar ratio of lithium to aluminum, Li:Al, is 30:70 to 80:20, andpreferably 35:65 to 50:50. Within this range, an α-LiAl phase, in whichaluminum is excessive, or a monophase of lithium is not easily formed inthe aluminum-lithium alloy by charge and discharge (see FIG. 7), andthereby an aluminum-lithium alloy layer 33 with an appropriate blendingratio can be formed.

The solid electrolyte layer 40 is formed by applying a solid electrolytematerial on an aluminum plate for forming the aluminum layer 31 in astep of applying a solid electrolyte material to be described below.

In this embodiment, the solid electrolyte layer 40 is a plate-likemember formed of a sulfide-based solid electrolyte material.

The sulfide-based solid electrolyte material is not particularlylimited, but the same materials as the sulfide-based solid electrolytematerials for use in the cathode electrode layer 20 can be used.

<Method for producing Solid-State Battery>

Subsequently, a method for manufacturing the solid-state battery 1according to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 8 is an explanatory view showing a method for manufacturing thesolid-state battery according to an embodiment of the present invention;and

FIG. 9 is an explanatory view illustrating an example of the cuttingstep in the method for manufacturing a solid-state battery according toone embodiment of the present invention.

As shown in FIG. 8, the method for manufacturing the solid-state battery1 comprises a solid electrolyte material application step, a pressjoining step and a cutting step.

[Solid Electrolyte Material Application Step]

The solid electrolyte material application step according to the presentembodiment is a step of applying a solid electrolyte material on analuminum plate for forming the aluminum layer 31, so as to form thesolid electrolyte layer 40.

Examples of the method of applying a solid electrolyte material includea die coating method, a spray coating method, a transfer sheet method, adip coating method, and a screen-printing method.

In the solid electrolyte material application step of the presentinvention, a solid electrolyte material is directly applied on analuminum plate for forming the aluminum layer. Thus, the solidelectrolyte material can be applied with high accuracy.

[Press Joining Step]

A press joining step according to the present embodiment is a step ofobtaining the solid-state battery 1 by press joining a laminate: withthe laminate being obtained by disposing the cathode electrode layer 20on the solid electrolyte layer 40 formed on one surface of an aluminumplate for forming the aluminum layer 31, and disposing a lithium platefor forming the lithium layer 32 on the other surface of the aluminumplate on which the solid electrolyte layer 40 is not formed.

In this embodiment, the battery body 10 is press joined by the pressjoining step using a roll pressing method, with the solid electrolytematerial being directly applied on the aluminum plate for forming thealuminum layer 31.

In the solid electrolyte material application step and the press joiningstep according to the present invention, a transfer sheet or the like ofa solid electrolyte material is unnecessary, nor are two or moreapplication steps of the solid electrolyte material necessary.

Thereby, a solid-state battery can be manufactured by a simple process.

Note that the press joining step can be carried out, for example, usinga uniaxial pressing method, etc., instead of the roll pressing method.

[Cutting Step]

A cutting step is a step of cutting the press joined battery body to apredetermined length.

As shown in FIG. 9, in the present embodiment, the cutting step is astep of cutting the press joined battery body 10 to a predeterminedlength under compression.

In the present embodiment, as shown in FIG. 9, when a punch is loweredby applying a force P from above the die hole, a compression force isapplied so that the battery body 10 is pressed down to the die.

Further, since there is a clearance so that the width of the die hole islonger than the width of the punch, a force F perpendicular to the forceP arises from a contact between the battery body 10 and the punch and acontact between the battery body 10 and the peripheral portion of thedie hole, and fissures are generated.

Therefore, continuous application of the force to the die hole fromabove develops fissures and the battery body 10 is cut to apredetermined length under compression.

In such a cutting step, no force is applied in the direction of peelingoff respective constituents of the battery body 10. As a result, voidsdo not easily occur between the respective constituents of the batterybody 10.

Further, since the battery body 10 is in a mechanism which is lesslikely to bend during cutting, the electrode position after punching isless likely to be displaced, and this facilitates lamination.

In this embodiment, as shown in FIG. 1, the battery body obtained bycutting is joined with the anode current collector 50 and the cathodecurrent collector 60 to give the solid-state battery 1 comprising theanode current collector 50 and the cathode current collector 60.

Further, the solid-state battery 1 may be repeatedly charged anddischarged.

The charge and discharge step advances alloying of aluminum and lithium(allows the aluminum-lithium alloy layer 33 to grow), and thesolid-state battery 1 is obtained in which the discharging capacity doesnot easily decline even after repeated charging and discharging.

EXAMPLES

Subsequently, the present invention will be described in further detailwith reference to the Examples, but the present invention is not limitedthereto.

Example 1

An aluminum foil having a thickness of 100 μm and a lithium foil havinga thickness of 100 μm were superposed to obtain an anode electrode layerof Example 1.

<Comparative Example 1>

Aluminum-lithium alloy powder was press molded to obtain an anodeelectrode layer of Comparative Example 1.

Solid-state batteries each incorporating an anode of Example 1 or ananode of Comparative Example 1 were prepared and used as solid-statebatteries for a cycle test.

These solid-state batteries were subjected to 20, 50 and 100 cycles ofcharge and discharge.

Also, before the charge and discharge and for each cycle, dischargingcapacity and DCR resistance were measured.

The results are shown in FIGS. 2 and 3.

Further, X-ray diffraction of the anode of Example 1 before the chargeand discharge and the anode of Example 1 after 100 cycles of charge anddischarge was performed from a cathode side (aluminum layer side).

The results are shown in FIG. 4.

Similarly, X-ray diffraction of the anode of Comparative Example 1 afterthe charge and discharge and the anode of Comparative Example 1 after100 cycles of charge and discharge was performed from the cathode side.

The results are shown in FIG. 5.

As shown in FIGS. 2 and 3, the solid-state battery of Example 1 using aplate-like (foil-like, thin film-like) anode electrode layer wasconfirmed to be more excellent than the solid-state battery using apowdery anode electrode layer in both the discharging capacity retentionrate and the DCR-resistance in each cycle.

Further, as shown in FIG. 4, formation of an alloy has not progressedbefore repeating charge and discharge in the solid-state battery ofComparative Example 1 which comprises a plate-like anode electrodelayer. An aluminum-lithium alloy layer with an appropriate blendingratio is considered to be formed as the charge and discharge isrepeated.

In contrast, as shown in FIG. 5, in the solid-state battery comprising apowdery anode electrode layer, aluminum decreased from the anodeelectrode layer due to charge and discharge.

Specifically, it is considered that as charge and discharge is repeated,a layer containing a large amount of aluminum (α-LiAl phase, β-LiAlphase) decreased, and was transformed to a lithium- excessiveLi1.92Al1.08 phase.

That is, since the present solid-state battery comprises an aluminumlayer in contact with a solid electrolyte layer, and a lithium layer incontact with the aluminum layer, it is considered that analuminum-lithium alloy layer with an appropriate blending ratio grows,as charge and discharge is repeated.

As a result, it is possible to provide a solid-state battery in whichthe discharging capacity does not easily decline even after repeatedcharging and discharging.

For the same reason, it is possible to provide a solid-state battery inwhich the DCR resistance does not easily increase even after repeatedcharging and discharging.

On the other hand, in the solid-state battery using a powdery anodeelectrode layer, aluminum decreased from the anode electrode layer aftercharge and discharge. This phenomenon is considered to be due to flowout of aluminum from the anode current collector side due to charging.Therefore, in the solid-state battery using a powdery anode electrodelayer, the discharging capacity is considered to keep on declining, ascharge and discharge are repeated. For the same reason, it is consideredthat the DCR-resistance will keep on increasing, as charge and dischargeis repeated in the solid-state battery using a powdery anode electrodelayer.

Example 2 to Example 6

An aluminum plate and a lithium plate were superposed so that thecontent of lithium was:

-   -   38 mol % (Example 2),    -   44 mol % (Example 3),    -   50 mol % (Example 4),    -   60 mol % (Example 5) or,    -   80 mol % (Example 6), respectively, provided that the total of        lithium and aluminum was assumed to be 100 mol %, to obtain        anode electrode layers of Example 2 to Example 6.

Solid-state batteries incorporating the anode electrode layers ofExample 2 to Example 6 were prepared in the same manner as in Example 1to obtain solid-state batteries for cycle tests.

With respect to these solid-state batteries, charge and discharge of 1to 100 cycles (1 to 20 cycles for Example 5 and Example 6) wasperformed.

Also, discharging capacity was measured before charge and discharge aswell as for each cycle.

The results are given in FIG. 6.

The results shown in FIG. 6 will be discussed with reference to FIG. 7.

Here, FIG. 7 is a phase diagram of a two-component aluminum-lithiumalloy.

According to FIG. 7, when the molar ratio of lithium to aluminum, Li:Al,is within the range of 30:70 to 80:20, it is difficult for an α-LiAlphase, in which aluminum is excessive, or a lithium monophase, to formin the aluminum-lithium alloy. In particular, within the molar ratio,Li:Al, of 35:65 to 50:50, a β-LiAl phase in which the molar ratio oflithium to aluminum is approximately 1:1 is easily formed in thealuminum-lithium alloy.

From the results of the cycle tests of Example 5 and Example 6 shown inFIG. 6, within the molar ratio of lithium to aluminum, Li:Al, of 30:70to 80:20, a declining tendency in discharging capacity retention ratesis recognized up to about 10 cycles. However, even when the charge anddischarge is further repeated, an α-LiAl phase or a lithium monophase isnot easily formed in the aluminum-lithium alloy. An aluminum-lithiumalloy layer having an appropriate blending ratio is considered to keepon growing by repeating the charge and discharge process.

Therefore, within the molar ratio, Li:Al, of 30:70 to 80:20, it ispossible to provide a solid-state battery in which discharging capacitydoes not easily decline even if charge and discharge are repeated.

Furthermore, from the results of the cycle tests of Example 2 to Example4 shown in FIG. 6, within the molar ratio of lithium to aluminum, Li:Al,of 35:65 to 50:50, as charge and discharge is repeated, a β-LiAl phaseis formed in the aluminum-lithium alloy, and an aluminum-lithium alloylayer with an appropriate blending ratio is considered to keep ongrowing.

Therefore, it is considered that, within the molar ratio of Li:Al of35:65 to 50:50, it is possible to provide a solid-state battery in whichdischarging capacity does not easily decline, even after repeatedcharging and discharging.

Example 7

On an electrode obtained by coating an aluminum plate with a solidelectrolyte layer in advance, an electrode coated with a cathode layerwas superposed and pressure molded at a pressure of 4.5 ton/cm2 in auniaxial press.

Thereafter, a lithium plate was placed under an anode electrode layerand pressure molded at a pressure of 1 ton/cm2 to prepare a solid-statebattery.

An aluminum plate having a thickness of 100 μm and a lithium platehaving a thickness of 100 μm were used as the anode electrode layer.

Comparative Example 2

A mixture electrode obtained by mixing hard carbon (anode activematerial) and a solid electrolyte at a ratio of 55:45 wt % was molded ina uniaxial press under a pressure of 3 ton/cm2.

The anode electrode layer after molding was coated with a solidelectrolyte layer.

Thereafter, an electrode coated with a cathode layer was superposed andpressure molded at a pressure of 4.5 ton/cm2 in a uniaxial press toprepare a solid-state battery.

With respect to the solid-state batteries of Example 7 and ComparativeExample 2, charge and discharge of 100 cycles was performed at a currentdensity of 1 mA/cm2 and cross-sectional layers of the anode electrodesafter the charge and discharge were observed by SEM.

Observation photographs are shown in FIGS. 10 and 11.

As shown in FIGS. 10 and 11, the solid-state battery of Example 7comprising a solid electrolyte material applied on an aluminum plate wasconfirmed to have a good junction interface formed at the interfacebetween the anode electrode layer and the solid electrolyte.

On the other hand, in Comparative Example 2 comprising a mixtureelectrode prepared from a mixture powder, considerable exfoliation wasconfirmed at the interface between the anode active material and thesolid electrolyte.

Specifically, as shown in FIG. 10, no exfoliation occurred between theanode electrode layer (aluminum plate) and the solid electrolyte ofExample 7, and it was confirmed that a good junction interface wasformed at the interface between the anode electrode layer and the solidelectrolyte.

Furthermore, in the anode electrode layer of Example 7, no voids wereconfirmed between the aluminum plate and the aluminum-lithium alloylayer, or between the aluminum-lithium alloy layer and the lithiumplate. That is, the anode electrode layer of Example 7 was confirmed tohave become a dense electrode layer.

On the other hand, as shown in FIG. 11, exfoliation was confirmed at theinterface between the anode electrode layer (anode active material) ofExample 7 and the solid electrolyte. Further, in the anode electrodelayer of Comparative Example 2, numerous voids were also confirmed atthe interface between the anode active material and the solidelectrolyte. That is, the anode electrode layer of Comparative Example 2was confirmed to be not densified as an electrode layer.

Therefore, the manufacturing method of Example 7 could performinterfacial junction between the solid electrolyte and the anode activematerial by a relatively lower battery restricting pressure than themanufacturing method of Comparative Example 2, and could provide alow-resistance and highly durable solid-state battery.

EXPLANATION OF REFERENCE NUMERALS

1 Solid-state battery

20 Cathode electrode layer

30 Anode electrode layer

31 Aluminum layer

32 Lithium layer

33 Aluminum-lithium alloy layer

40 Solid electrolyte layer

1. A solid-state battery comprising a cathode electrode layer, an anodeelectrode layer and a solid electrolyte layer disposed between thecathode electrode layer and the anode electrode layer, wherein the anodeelectrode layer comprises an aluminum layer in contact with the solidelectrolyte layer, a lithium layer and an aluminum-lithium alloy layerdisposed between the aluminum layer and the lithium layer.
 2. Thesolid-state battery according to claim 1, wherein a film thickness ofthe anode electrode layer is 10 to 400 μm.
 3. The solid-state batteryaccording to claim 1, wherein a molar ratio of lithium to aluminum,Li:Al, in the anode electrode layer is 30:70 to 80:20.
 4. Thesolid-state battery according to claim 1, wherein the solid electrolytelayer is a sulfide-based solid electrolyte material.
 5. A method formanufacturing a solid-state battery comprising a cathode electrodelayer, an anode electrode layer comprising an aluminum layer and alithium layer, and a solid electrolyte layer disposed between thecathode electrode layer and the anode electrode layer, the methodcomprising: a step of applying a solid electrolyte material to analuminum plate for forming the aluminum layer to form the solidelectrolyte layer; and a step of press joining a laminate to obtain thesolid-state battery, with the laminate being obtained by disposing thecathode electrode layer on the solid electrolyte layer formed on onesurface of the aluminum plate, and, disposing a lithium plate forforming the lithium layer on the other surface of the aluminum plate onwhich the solid electrolyte layer is not formed.
 6. The method formanufacturing a solid-state battery according to claim 5, wherein themethod further comprises a step of cutting the press joined solid-statebattery to a predetermined length under compression.
 7. The method formanufacturing a solid-state battery according to claim 5, wherein thepress joining is performed by a roll pressing method.
 8. The solid-statebattery according to claim 1, wherein a film thickness of the anodeelectrode layer is 10 to 400 μm, wherein a molar ratio of lithium toaluminum, Li:Al, in the anode electrode layer is 30:70 to 80:20.
 9. Thesolid-state battery according to claim 1, wherein a film thickness ofthe anode electrode layer is 10 to 400 μm, wherein the solid electrolytelayer is a sulfide-based solid electrolyte material.
 10. The solid-statebattery according to claim
 1. wherein a molar ratio of lithium toaluminum, Li:Al, in the anode electrode layer is 30:70 to 80:20, whereinthe solid electrolyte layer is a sulfide-based solid electrolytematerial.
 11. The solid-state battery according to claim 1, wherein afilm thickness of the anode electrode layer is 10 to 400 μm, wherein amolar ratio of lithium to aluminum, Li:Al, in the anode electrode layeris 30:70 to 80:20, wherein the solid electrolyte layer is asulfide-based solid electrolyte material.
 12. The method formanufacturing a solid-state battery according to claim 5, wherein themethod further comprises a step of cutting the press joined solid-statebattery to a predetermined length under compression, wherein the pressjoining is performed by a roll pressing method.